An odd-looking white bear with patches of brown fur was shot by hunters in 2006 and found to be a cross between a polar bear and a grizzly bear. Apparently, grizzlies were moving north into polar bear territory. Since then, several hybrid animals have appeared in and around the Arctic, including narwhal-beluga whales and mixed porpoises.

The culprit may be melting Arctic sea ice, which is causing barriers that once separated marine mammals to disappear, while the warming planet is making habitats once too cold for some animals just right. The resulting hybrid creatures are threatening the survival of rare polar animals, according to a comment published Wednesday (Dec. 15) in the journal Nature. [Real of Fake? 8 Bizarre Hybrid Animals]